TWI517620B - Method and apparatus for communicating in a mimo network - Google Patents

Description

Method and apparatus for communicating in a multiple input multiple output (MIMO) network

The present invention relates to a method for communicating in a communication network. More specifically, the present invention relates to a method of communicating between a primary station and one or more secondary stations in a MIMO (Multiple Input Multiple Output) mode. The invention is also directed to a primary or secondary station on which such a method can be implemented.

For example, this invention relates to all wireless communication networks, and in one example described below, it relates to a mobile telecommunications network, such as UMTS or UMTS LTE.

In communication networks, MIMO (Multiple Input, Multiple Output) has been widely proposed to increase the amount of communication throughput that can be achieved. MIMO involves the use of multiple antennas in both the transmitter and the receiver to improve communication performance. In fact, there is a significant increase in data throughput with higher spectral efficiency (more bits per Hz bandwidth) and link reliability without the need for additional bandwidth or transmission power.

Multi-user MIMO (MU-MIMO) is an advanced MIMO that allows one station to simultaneously communicate with multiple users in the same frequency band. In an exemplary embodiment of the present invention, a mobile communication network includes a primary station (base station or NodeB or eNodeB), and the primary station can use a plurality of primary station antennas and a plurality of secondary station antennas At the same time, it communicates with a plurality of sub-stations (mobile stations or user equipments or UEs) in MIMO stream. To form the stream, the secondary stations provide information about the status of the channel to the primary station by transmitting CSI (Channel Status Information) back to the primary station. The CSI indicates one of the best or at least one preferred precoding vector to be used to maximize the achievable data rate of the corresponding spatially separable data stream transmitted by the primary station. The precoding vector may be a set of complex values applied to each of the antennas of the primary station during transmission to direct the data stream to one of the secondary station antennas.

However, in the context of MU-MIMO, when a signaled precoding vector is used, one of the sub-stations that simultaneously communicate with the primary station can be caused to interfere with one of the beams. In addition, the secondary station cannot assess where the interfering stations are located and whether the use of a precoding vector can cause interference. Sharing the precoding vectors transmitted by the secondary stations in each of the secondary stations will cause too much signal transmission and will require too much computational power of each secondary station to produce interference free precoding vectors.

It is an object of the present invention to provide an improved method of communicating in a MU-MIMO network that mitigates the problems described above.

Another object of the present invention is to provide a method of communication that does not cause too much signal transmission when channel quality is enhanced by reducing interference.

Yet another object of the present invention is to provide a system that includes a primary station and a plurality of secondary stations that can maximize the amount of data transported throughout the system.

To achieve this object, in accordance with an aspect of the present invention, a method of communicating in a network is provided, the network comprising a primary station and at least a first secondary station, wherein the first secondary station will be the first plurality One of the precoding vectors indicates transmission to the primary station, wherein the number of first precoding vectors is greater than the preferred transmission rank from one of the primary stations to the first secondary station.

The transmission rank means the number of spatially separable data streams for MIMO communication between the primary station and a given secondary station. It should be noted that the rank may not exceed the minimum number of antennas of the primary station and the number of antennas of the secondary station. For example, a sub-station with one of four antennas cannot receive more than four spatially separable streams and therefore cannot exceed the fourth rank communication. In addition, one of the 16 antennas can not transmit more than 16 beams. As an example, the primary station can simultaneously transmit four fourth rank MIMO transmissions to four secondary stations, or one fourth rank MIMO transmission to one secondary station, and transmit to two other second secondary MIMOs by two second rank MIMO. The station, and 8 first rank MIMO transmissions to another eight substations.

Thus, for example, the primary station can generate another precoding vector based on linearly combining one of the indicated plurality of vectors to establish communication. In the case of an MU-MIMO embodiment, the primary station can now generate a precoding vector, which may be sub-optimal from the perspective of the secondary station, but the precoding vector allows for transmission to different pairs. Interference between the stations. In a particular embodiment, the primary station selects a combination of precoding vectors, such as one of the linear combinations that do not require extensive processing, such that the sum of all transmission rates of the connected secondary stations is maximized.

According to another aspect of the present invention, a secondary station is provided, the secondary station comprising means for communicating with a primary station in a network, the secondary station further comprising a transmission member configured to transmit the first plurality One of the precoding vectors indicates transmission to the primary station, wherein the number of first precoding vectors is greater than the preferred transmission rank from one of the primary stations to the first secondary station.

These and other aspects of the invention will be apparent from the description of the <RTIgt;

The invention will now be described in more detail by way of example with reference to the accompanying drawings.

The present invention relates to a communication network having a primary station and a plurality of secondary stations in communication with the primary station. This network is illustrated, for example, in Figures 1 and 2, in which a primary or base station 100 is in wireless communication with a plurality of secondary stations 101, 102, 103, and 104. In an illustrative example of the invention, the secondary stations 101-104 are user devices of a mobile station or a UMTS network.

According to a first embodiment of the present invention, the primary station 100 includes an antenna array including a plurality of antennas and a complex gain amplifier such that the primary station 100 can perform beamforming, such as MIMO beamforming. Typically, the primary station includes 4 antennas. In most advanced LTE releases, the primary station may include 8 antennas, 16 antennas or more. Similarly, for those UEs that are compliant with the first LTE version, the secondary stations 101-104 include a plurality of antennas, for example, 2 antennas. In later versions, the secondary stations may have 4 or 8 antennas, or even more antennas. Due to the antenna arrays, the primary station 100 can form a beam of data streams, such as beams 150 and 151 as depicted in FIG. In order to form a beam and construct a MIMO communication, a precoding vector must be generated, which requires information about the state of the channel and calculations on both the secondary station side and the primary station side.

For example, in the first version of the LTE specification, a sub-station that is configured to receive downlink transmissions in MU-MIMO performs downlink channel measurements (typically using a common reference signal (CRS) that is not precoded) Channel status information (CSI) feedback is transmitted to the primary station (the eNodeB). This indicates a preferred precoding vector (PMI, Precoding Matrix Indicator) to be used for the downlink transmissions and an associated CQI (Channel Quality Information) value indicating one of the corresponding modulation and coding schemes. In this example, the downlink transmissions are based on a codebook, which means that the precoding vectors for transmission are selected from a finite set. The selected precoding vector is signaled to the secondary stations such that the secondary station can derive a phase reference as a linear combination of one of the common reference signals (CRS).

A sub-station having a single receive antenna returns an index of a single preferred precoding vector that enables better quality transmission or most reliable communication, for example, maximizing signal-to-interference at its antenna One of the ratio SINR precoding vectors. This may be based on one of the transmit beamforming vectors, a predetermined codebook, or direct channel vector quantization (CVQ). If the secondary station has two (or more) receive antennas, the situation is more complicated and the approach taken depends on the codebook size available for quantized CSI feedback. The action done at this sub-station will be to feed back the entire channel matrix (or at least one of the quantized versions of the feedback channel matrix). However, this requires significant signaling of additional overhead and resources.

In the case of the second rank transmission, it is possible to feed back a preferred precoding matrix. However, if, for example, the rank of the channel matrix is limited, the secondary station prefers the first rank transmission, or if the secondary station is configured to support only one of the first rank transmission MIMO modes, Or if the primary station only schedules a first rank transmission, this is not appropriate.

For the first rank transmission, in the case of a relatively small feedback codebook, one of the two receiving antennas can determine a single preferred precoding vector by deriving the received combining vector, which maximizes the codebook. The SINR of each transmit beamforming vector. This single preferred precoding vector can typically be a MMSE (Minimum Mean Square Estimation) receive combining vector. The UE may report the transmit beamforming vector that maximizes the maximum SINR.

For a single stream to one of the stations, this method can be expressed as follows:

1. The received signal is given by y = Hg x + n , where

o y is the received signal, is an N × 1 vector

The signal transmitted by the o x is a 1×1 vector

o g is a precoding vector, which is M×1

o H system channel matrix, N × M

o n is the noise of each receiving antenna, which is an N × 1 vector. For convenience, H can be normalized to make the noise variance equal.

o M is the number of transmission antennas in the eNB

o N is the number of receiving antennas in the UE

2. For each possible g in a codebook of size C, calculate the receive antenna weight vector w(1xN) such that wy = Minimize the error E [ x - ], that is, w = ( Hg ) ^H (( Hg ) ( Hg ) ^H + σ ² I ) ^-1 .

3. After calculating the corresponding MMSE solution for w, report the maximal SINR g. This is equivalent to reporting g of a single receive antenna, where g is selected to maximize the received SINR of one of the valid 1 x M transmission channels given by wH.

4. The eNB scheduler will select UE pairs that report orthogonal g's (or at least g's with low correlation).

In the case of channel vector quantization (CVQ) based feedback, a similar approach may result in a single preferred precoding vector for the feedback. However, this relies on one of the assumptions of zero-forcing beamforming at the primary station transmitter and is dependent on an approximation of the generated SINR.

The main drawback of the above methods is that the above methods do not necessarily maximize the sum rate in one cell of MU-MIMO, because different pairs of UEs can achieve a higher sum rate by selecting one w, However, the SINR of each individual UE is not maximized.

This can be illustrated in the beam 151 that is directed from the primary station 100 to the secondary station 101 as shown in FIG. Even though this beam 151 is one of the SINRs that maximizes the SINR of the secondary station 101, the beam causes significant interference to the secondary station 102. Because the beam 151 directed to this sub-station 102 is directed so that the secondary station 102 will not be able to communicate with one of the high SINRs.

Moreover, in some cases, the secondary station may not perform computation to optimize a single weight vector w of the SINR, and thus may not implement feedback to a single preferred transmission precoding vector, such as:

i) a large feedback case, making different optimization numbers and SINR calculations expensive;

Ii) The secondary station does not understand the transmission of the precoding vector, for example:

a. transmit beamforming at the primary station, wherein the phase reference is given by a precoded reference signal, rather than by a CRS and one of the actually used precoding vectors; in this case, In fact, there are an infinite number of transmission precoding vectors available. For each transmission precoding vector, the secondary station must derive the optimal weight vector w;

b. Feedback based on channel vector quantization when one of the assumptions of zero-transmission beamforming may not necessarily be valid.

One aspect of the present invention is based on the fact that for such situations identified above, there may be a large or even an infinite number of w. This means that by changing w, the base station may choose to maximize the UE rate of the sum rate, but not necessarily maximize the rate of any individual UE.

An exemplary variation of a first embodiment of the present invention is depicted in FIG. 2, wherein the primary station 100 can direct the beam 151 such that the secondary station 102 is undisturbed by the beam. Even if the beam 151 does not give the highest possible SINR value to the secondary station 101, the achievable sum rate of all of the secondary stations may be better because the secondary station 102 is not exclusively used for another secondary station ( That is, the interference of the light beam 151 of 101).

To achieve this object, according to a first embodiment of the present invention, it is proposed that the secondary station feeds back a set of preferred precoding vectors to the primary station, the number of precoding vectors being greater than the rank of the preferred transmission. The primary station may first determine the preferred transmission rank and pre-configure the secondary station. This then allows the secondary station to be aware of the number of required precoding vectors that need to be fed back to the primary station. It is also allowed to limit the calculation requirements at the secondary station, and the secondary station will be more limited in terms of computing power than the primary station.

However, it may be possible for the secondary station to make a decision on the preferred transmission rank depending on the channel status such that it allows one of the channels to be optimally used. In this case, the secondary station signals the preferred transmission rank to the primary station.

According to a variant of the first embodiment, when applied to a secondary station or two receiving antennas of a UE in an LTE network, even when the first rank transmission is preferred, each UE returns two Precoding vector g' s ( g ₁ and g ₂ ). Each precoding vector g can be calculated as above by selecting two preferred orthogonal receive vectors w ₁ and w ₂ , the two preferred orthogonal receive vectors w ₁ and w _{2 being} known to both the master station and the secondary station Or it has a relationship known to both the primary station and the secondary station, and the relationship may be a prior relationship.

According to an advantageous embodiment, the first received vector w ₁ is calculated to maximize the rate of one of the codebook based feedback methods as described above. This w value is also used to calculate a corresponding CQI value that gives sufficient information to the situation when no other sub-station is last scheduled to transmit at the same time. The second vector w ₂ can then be selected as an orthogonal vector of w ₁ (which gives sufficient information for optimal scheduling of another secondary station), and a second CQI value is calculated for this w value and will also Its feedback. The secondary station also returns the corresponding g values ( g ₁ and g ₂ ).

For two receive antennas at the secondary station, for example, a suitable embodiment may use w vectors w ₁ = [1 1] and w ₂ = [1 -1], or [0 1] and [1 0 ] to correspond to the receiving antenna selection.

It should be noted that this exemplary embodiment of the present invention can be extended to a sub-station having one of the N receive antennas, in which case w is a dimension 1 x N one vector. In this case, the secondary station can transmit better precoding vector feedback corresponding to up to N w vectors. For example, if N=4, the secondary station can feed back four preferred precoding vectors corresponding to w ₁ , w ₂ , w _{3 ,} and w ₄ , for example, all of the vectors can be orthogonal to each other.

According to a variant of the above example, the secondary station can transmit a reduced amount of feedback corresponding to less than N w 's. In this case (eg, 2 w 's), which particular w 's are selected may take into account the correlation between the receive antennas to maximize the information fed back to the primary station.

For example, if w ₁ is selected to maximize the rate, the possible multipliers used to generate w ₂ , w _{3 ,} and w ₄ may be [1 1 -1 -1], [1 -1 1 -1] And [1 -1 -1 1]. The antennae system is assumed to separate indexed sequential (and therefore related), for use w w w _{4 2. 3} or system may be preferred (i.e., eNodeB which will give more).

As a further aspect of the present invention, the secondary station selects the second w according to the correlation between the antennas (because the primary station does not need to know the relationship between the antenna index and the physical antenna at the secondary station) .

In another embodiment, the secondary station selects and feeds n ws with the highest SINR, where n < N.

As a further example, if w ₁ is selected as [1 1 1 1], the possible values of w ₂ , w ₃ and w ₄ may be [1 1 -1 -1], [1 -1 1 -1] And [1 -1 -1 1].

In one embodiment of N=2, the master station scheduler is free to select any g _{A of} user _A , which is linearly combined as one of g ₁ and g ₂ of orthogonalization g _A , and user B One is similarly deduced g _B . This can be extended to N>2, where the secondary station reports two (or more) g values, and the eNB applies precoding of a linear combination of one of the reported values.

If the secondary station reports N g values corresponding to N w values, then this will provide some information about the complete channel matrix to the eNB. However, this has some advantages over known methods because there is no need to specify the ordering of the receiving antennas, and for the same accuracy of the channel representation, the computational complexity may be lower (ie, the size is one of the C codes) The N searches of the book are compared to a search of one size of the CN codebook).

In a variant of the invention, the primary station is a mobile terminal such as a user equipment, and the primary station is a base station such as an eNodeB.

The invention may be applicable to mobile telecommunications systems such as UMTS LTE and advanced UMTS LTE, but in some variations, the invention is also applicable to any communication system that automates the configuration of resources or at least semi-continuously completes the configuration of resources.

In the specification and claims, the word "a" or "an" In addition, the word "comprising" does not exclude the presence of the elements or the steps in the

The reference signs contained in parentheses in the scope of the patent application are intended to aid understanding and are not intended to be limiting.

Other modifications will be apparent to those skilled in the art from reading this disclosure. Such modifications may include other features known in the art of radio communication.

100. . . Main station

101. . . Secondary station

102. . . Secondary station

103. . . Secondary station

104. . . Secondary station

150. . . Beam

151. . . Beam

1 is a block diagram of a network for maximizing the rate of a sub-station according to a beamforming scheme;

2 is a block diagram of a network in accordance with an embodiment of the present invention.

100‧‧‧Main station

101‧‧‧Sub-station

102‧‧‧Sub-station

103‧‧‧Sub-station

104‧‧‧Sub-station

150‧‧‧beam

151‧‧‧beam

Claims (17)

A method for communicating in a network, the network comprising a primary station and at least a first secondary station, wherein the first secondary station transmits a first plurality of precoding vectors to the primary a station, wherein the indication comprises a number of one of the precoding vectors in the first plurality of precoding vectors, the number being greater than a rank of transmission from the primary station to the first secondary station. The method of claim 1, wherein the transmission rank is signaled to the primary station by the first secondary station. The method of claim 1, wherein the transmission rank is configured by the primary station. The method of claim 1, wherein the transmission rank is determined in advance. The method of any one of claims 1 to 4, wherein the first secondary station derives each of the precoding vectors of the first group based on a different corresponding received combined vector. The method of claim 5, wherein the received combination vectors are orthogonal to one another. The method of claim 5, wherein a transmission rate at which at least one precoding vector of the first group and the corresponding received combined vector are reached is transmitted to the primary station. The method of claim 5, wherein the transmission rates that can be achieved by each of the first set of precoding vectors and their corresponding received combination vectors are transmitted to the primary station. The method of any one of claims 1 to 4, wherein the number of the first plurality of precoding vectors is less than the number of receiving antennas of the secondary station. The method of claim 9, wherein the secondary station selects the first plurality of precoding vectors depending on at least one of: the correlation between the receiving antennas of the secondary station; and one of each precoding vector Corresponds to SINR. The method of any one of claims 1 to 4, further comprising the step of: the primary station selecting a first transmission precoding vector based on a combination of the first plurality of precoding vectors of the first group. The method of claim 11, wherein the step further comprises: selecting a second transmission precoding vector based on a combination of the second precoding vectors of the second set of precoding vectors, the second sub station indicating the Two sets of precoding vectors, and wherein the first transmission precoding vector and the second transmission precoding vector are selected such that a summation rate of the first sub station rate and the second sub station rate is maximized. The method of claim 12, wherein the first transmission precoding vector is substantially orthogonal to the second transmission precoding vector. The method of any one of claims 1 to 4, wherein each of the transmission precoding vectors is a linear combination of the precoding vectors of the respective groups. A secondary station comprising means for communicating with a primary station in a network, the secondary station further comprising transmissions configured to transmit a first plurality of precoding vectors to the primary station And means, wherein the indication comprises a number of one of the first plurality of precoding vectors in the first plurality of precoding vectors, the number being greater than a transmission rank from the primary station to the first secondary station. A primary station includes means for communicating with at least one secondary station in a network, the primary station further comprising: a receiving member configured Receiving, by the at least one secondary station, an indication of one of the first plurality of precoding vectors, wherein the indication includes a number of one of the precoding vectors in the first plurality of precoding vectors, the number being greater than from the primary station One of the first secondary stations transmits a rank; and a control component configured to select a first transmitted precoding vector based on a combination of the first set of the first precoding vectors of the first set. A communication system includes a primary station and at least one secondary station, the at least one secondary station further comprising: a transmission component configured to transmit a first plurality of precoding vectors to the primary station. Wherein the indication comprises a number of one of the precoding vectors in the first plurality of precoding vectors, the number being greater than a transmission rank from the primary station, the at least one secondary station obtaining the transmission rank.